Fuses with casings of synthetic-resinglass-cloth-laminates



May 28, 1957 P. c. JACOBS, JR 2,794,098

FUSES WITH CASINGS OF SYNTHETIC-RESIN-GLASS-CLOTH-LAMINATES Filed Feb. 14, 1955 Invezaoai' C. JaCOZhSJ-i".

Unite States FUSES WITH CASNGS Gli? SYNTHETEC-RESN- GLASS-CLOTH-LANHNA'EES Philip C. Jacobs, Jr., Newtonville, Mass., assigner to The Chase-Shawmut Company, Newburyport, Mass.

This invention relates to fuses, and more particularly to high rupturing-capacity current-limiting fuses of very compact design having casings of synthetie-resin-glasscloth-laminates.

Synthetic-resin-glass-cloth-laminates have a high heatshock resistance, a high dielectric and bursting strength, are not subject to tracking, and have still other properties which make them particularly desirable as materials for casings of fuses wherein extremely high pressures are generated on account of a drastic reduction of size or volurne. The prior art current-limiting `fuses of drastically reduced size or volume whose synthetic-resin-glass-clothlaminate casings have suiiicient bursting strength to withstand the high pressures generated incident to blowing of the fuses are subject to serious limitations regarding the terminal elements by which their casings are closed and the connectors associated with the terminal elements.

It is, therefore, one object of this invention, to provide high rupturing-capacity current-limiting fuses of very compact design having casings of a synthetic-resin-glass-clothlaminate whose terminal elements and associated connectors are not subject to the limitations inherent in prior art fuses of this type.

In certain prior art current-limiting Ifuses having casings of synthetic-resin-glass-cloth-laminates the danger of mechanical failure on account of the high internal transient pressures incident to blowing of the fuses is shifted from the casing to the terminal elements. In other words, the terminal elements are less pressure resistant or have a smaller bursting strength than the casing and there is a tendency of blowing the terminal elements ot the casing when very high pressures are generated in the latter on the occurrence of particularly severe arcing conditions. To avoid this danger, various special terminal element and connector designs have been evolved. All these designs provide the requisite mechanical strength of the terminal elements at the expense of considerable mechanical complications.

It is, therefore, another object of the invention to provide fuses of the aforementioned type avoiding the rnechanical complications to which comparable current-limiting fuses are subject.

The fuses disclosed in United States Patent 2,594,315 to Frederick I. Kozacka, April 29, 1952, Current-Limiting Fuse, comprise triple caps on each end of the casing to withstand the very high pressures generated therein.

It is another object of this invention to provide currentlimiting fuses capable of withstanding internal pressures of the same magnitude as those disclosed in the above patent without resorting to a relatively complicated and expensive triple cap design.

Compact low-voltage high rupturing-capacity fuses designed for high ampere ratings, say in excess of amps., have gener-ally terminal elements of the type shown in United States Patent 2,670,418 to Frederick l. Kozacka, February 23, 1954, Fuse and Fuse Holder. According to this patent the ends of a casing are closed by massive cylindrical metal blocks tted into and closing both ends of the casing. These metal blocks are secured to the casing by `a plurality of steel pins extending transversely through the casing into the metal blocks. These steel pins combined with the considerable inertia inherent in the metal blocks preclude the metal blocks from being pushed out of the casing under the action of the high transient pressures developed therein. Since it is not to produce tubing of synthetic-resin-glass-clothlaminates whose tolerances are sufficiently close to provide a gas-tight lit between the cylindrical terminal blocks and the inner surface of the casing, structures of the type disclosed in the above patent require either additional machining or provision of additional gas-tight seals such as, for instance, so called O-rings, between the casing and the terminal blocks.

lt is, therefore, another object of this invention to provide very compact high rupturing-capacity fuses having synthetic-resin-glass-cloth-laminate casings which fuses require no machining of the casing to tit the terminal elements into it, require no additional seals for producing a gas-tight t between the terminal elements and the casing, and do not rely on mass and inertia to preclude the terminal elements from being blown on the casing in case of very severe interrupting conditions.

Another object of the invention is to provide very compact light weight high rupturing-capacity fuses having synthetic-resin-glass-cloth-laminate casings.

Another object of the invention is to provide fuses capable of withstanding very high internal pressures by virtue of terminal caps riveted to the casing by plain rivets, as distinguished from blind rivets of which only one of the heads is accessible.

Other objects and advantages of the invention will, in part, be obvious and in part appear hereinafter.

For a more complete understanding of the nature and scope of this invention reference may be had to the following detailed description thereof taken in connection with the accompanying drawings, in which:

Fig. 1 is a View, partly in longitudinal section and partly in side elevation, showing a current-limiting fuse embodying the invention;

Fig. 2 is an end view of the structure shown in Fig. l seen in the direction of the arrow R;

Fig. 3 is a view, partly in longitudinal section and partly in side elevation, of another current-limiting fuse embodying the invention; and

Fig. 4 is an end view of the structure shown in Fig. 3 seen in the direction of the arrow R.

Referring now particularly to Figs. 1 and 2 of the drawings, it will be observed that the reference character 1 designates a tubular casing. This casing is made of a suitable synthetic-resin-glass-cloth laminate. The synthetic resin may, for instance, be one pertaining to the melamine or one pertaining to the silicone resin family. Arranged within casing 1 are two ribbon-type multiperforated fuse links 2 made of a high conductivity low fusing energy metal to minimize the amount of metal vapor evolved incident to blowing of the fuse `and to achieve fusion of the linl; as soon as possible after inception of a major fault. Silver and copper are the only metals which combine these properties to a sulhcient degree. Reference numerals 3, 3 have been applied to a pair of metal caps conductively interconnected by fuse links 2. Metal caps 3 are accommodated substantially within casing 1. The ends or circular edges of caps 3 remote from the bottom 3a thereof protrude from the axially outer ends of casing 1. The fuse comprises further a pair of connectors 4, 4 for inserting the same into a fuse holder, or equivalent contact structure. Connectors 4 each comprise a plate having a circular punched out portion 4a the inner diameter of which is equal to the outer diameter of caps 3. Connectors 4 are mounted upon the ends of caps 3 protruding beyond the axially outer ends of casing 1. The axially outer edges 3b of caps 3 are bent and rolled yaround the circular edge portions 4a of connectors 4 to firmly maintain the :latter in proper position, i. e. to clamp the connectors 4 against the axially outer ends of casing 1. Caps 3 are pushed under considerable pressure into casing 1 and are held in position by a plurality of angularly displaced rivets 5 projecting transversely across casing 1 and caps 3. Rivets 5 maintain caps 3 in position against the action of pressure developed in casing 1 incident to blowing of the fuse. Since both ends of rivets 5 are accessible, plain rivets may be and are 'being used, as distinguished from blind rivets. Blind rivets must Ybe used where Vit is not possible to provide an upset rivet head on both ends of each rivet shank. Figs. 1 and 2 show clearly rivets having an upset head on both ends of the shankthereof.

Links 2 maybe conductively connected to caps 3 in any desired manner. According to Fig. vl links 2 are inserted into grooves 3c providedV in the juxtaposed' surfaces of caps 3. Soft solder connections provided in the Vlinkreceiving grooves 3c between caps 3 and links 2 tend to minimize ythe resistance of the current path through the fuse. If desired, caps 3 may be spaced by a spacer plate 6 of a heat resistant insulating material which may have a glass-'cloth-base. The ends lof spacer plate 6 may be inserted into appropriate grooves provided in the juxtaposed surfaces of caps 3.

Where Athe arc energy dissipated in the fuse is relatively large, casing 1 ought to be filled with an energy absorber, preferably in the form of a body of reasonably pure quartz sand 7. Quartz sand 7 may be lled into casing l'through a small circular gap left between casing 1 and one of the caps 3 in the process of assembling the fuse. This gap is closed upon filling the quartz sand 7 into casing 1 when the latter is shoved to its ultimate position shown in Fig. 1.

As au alternative the pulverulent arc-quenching filler 7 may be filled into casing 1 through a hole (not shown) in one of caps 3 which is then closed by an appropriate seal.

In the structure shown no machining of casing 1 is required. A perfectly gas-tight fit of, and a connection having considerable mechanical strength between, caps 3 and casing 1 is achieved, even though the latter is made of sections of tubing of a synthetic-resin-glass-clothlaminate which cannot'be manufactured to close tolerances. Caps 3 even if made sufficiently strong to Withstand the highest pressures that casing 1 can withstand, have sufficient resiliency to achieve a gas-tight fit in casing 1, precluding the emission of hot products of arcing. If desired, caps 3 may be radially expanded upon being pushed under considerable pressure into casing 1, which tends to improve the t between the two parts.

In Figs. 3 and 4 the same reference characters as in Figs. l and 2 have been applied to indicate like parts. Figs. 3 and 4 thus call for a separate description only to the extent that the structure shown therein differs from that shown in Figs. 1 and 2.

According rto Figs. 3 and 4 the connectors 4, 4 form blade contacts arranged in planes transverse to casing 1. These blades engage fuse holders 8, 8 in the form of substantially U-shaped metal clips.

There are Vinstances where a casing of a fuse may be fitted with different terminal elements on either end thereof, and fuses of this type are intended to lie Within the spirit and scope of this invention though only one end thereof has 4terminal and connector means of the nature shown in Figs. 1 to 4.

Since certain further changes can be made in the foregoingrconstructions and different embodiments of the invention can be made without departing from the ,spirit and scope thereof, it is intended that all matter shown in the accompanying drawings and described hereinbefore shall be interpreted as illustrative and not in a limiting sense.

What is claimed as new is:

1. A current-limiting fuse comprising in combination a ribbon-type high conductivity low fusing energy fuse link means, a substantially tubular casing of a syntheticresin-glass-cloth-laminate housing said fuse link means, a pair of metal caps conductively interconnected by said fuse link means tightly fitting into said casing and accommodated substantially within said casing, the ends of said pair of caps remote from the bottom thereof being arranged adjacent to the axially outer endsof said casing, and a plurality of angularly displaced rivets projecting transversely across said casing and said pair of caps, each of said plurality of rivets having an upset head on both ends of the shank thereof.

2. A current-limiting fuse comprising in combination ribbon-type fuse link means at least in part of silver, a substantially tubular casing `.of a synthetic-resin-glasslaminate housing said fuse link means, a pulverulent quartz filler within said casing, means for closing both ends of said casing including a metal cap directly engaging and tightly tting the internal surface of said casing, said cap having a closed bottom end situated inside of said casing and an open end substantially coextensive with one of the axially outer ends l.of said casing, and a plurality of angularly displaced rivets projecting transversely across said casing and said cap, each of said plurality of rivets having an upset head on both ends of the shank thereof.

3. A current-limiting fuse comprising in combination a ribbon-type high conductivity low fusing energy fuse link means, a substantially tubular casing of syntheticresin-glass-cloth-laminate housing said fuse link means, a pair of metal caps conductively interconnected by said fuse link means accommodated substantially within said casing, the ends of said pair of caps remote from the bottom thereof protruding out of said casing at the axially outer ends thereof, a pair of connectors each having a circular edge portion in cooperative engagement with one of said pair of caps, each of said pair of connectors being held in position by an edge of one of said pair of caps bent around said circular edge portion of each of said pair of connectors, and a plurality of angularly displaced rivets projecting transversely across said casing and said pair of caps to maintain said pair of caps and said pair of connectors in position against the action of pressure generated in said casing.

4. A currentlimiting fuse comprising in combination a yribbon-type fuse link means at least in part of silver, a substantially tubular casing of synthetic-resin-glass-clothlaminate housing said fuse link means, at least one end of said casing being closed by a metal cap directly engaging and tightly tting the internal surface of said casing, the end of said cap remote from the bottom thereof being arranged adjacent to and protruding beyond one of the axially outer ends of said casing, a connector having a circular edge portion in engagement with said cap held in position by said end of said cap bent around said circular edge portion, and a plurality of angularly displaced rivets projecting transversely across said casing and said cap, each of said plurality of rivets having an upset head on both ends of the shank thereof.

5. A current-limiting fuse comprising in combination ribbon-type high conductivity low fusing energy fuse link means, a substantially tubular casing of synthetic-resinglass-cloth-laminate housing said fuse link means, a pair of metal caps conductively interconnected by said fuse link means accommodated substantially within said casing, the ends of said pair of caps remote from the bottom thereof being arranged adjacent to and protruding beyond the axially outer ends of said casing, a pair of connectors each having a circular aperture equal in diameter to the outer diameter of said pair of caps each mounted on the `axially outer end of one of said pair of caps, each of said 5 pair of connectors being held in position by an edge of one of said pair of caps bent around said circular aperture, and a plurality of angularly displaced rivets projecting transversely across said casing and said pair of caps,

each of said plurality of rivets having an upset head on 5 both ends of the shank thereof.

References Cited in the le of this patent UNITED STATES PATENTS Young Dec. 10, 1912 Jung Nov. 13, 1917 Steele Nov. 8, 1921 Smith Sept. 5, 1939 Komcka Jan. 5, 1954 

1. A CURRENT-LIMITING FUSE COMPRISING IN COMBINATION A RIBBON-TYPE HIGH CONDUCTIVITY LOW FUSING ENERGY FUSE LINK MEANS, A SUBSTANTIALLY TUBULAR CASING OF A SYNTHETICRESIN-GLASS-CLOTH-LAMINATE HOUSING SAID FUSE LINK MEANS, A PAIR OF METAL CAPS CONDUCTIVELY INTERCONNECTED BY SAID FUSE LINK MEANS TIGHTLY FITTING INTO SAID CASING, AND ACCOMMODATED SUBSTANTIALLY WITHIN SAID CASING, THE ENDS OF SAID PAIR OF CAPS REMOTE FROM THE BOTTOM THEREOF BEING ARRANGED ADJACENT TO THE AXIALLY OUTER ENDS OF SAID CASING, AND A PLURALITY OF ANGULARLY DISPLACED RIVETS PROJECTING TRANSVERELY ACROSS SAID CASING AND SAID PAIR OF CAPS, EACH OF SAID PLURALITY OF RIVETS HAVING AN UPSET HEAD ON BOTH ENDS OF THE SHANK THEREOF. 